The present invention relates to duplex printing devices and methods and, more particularly, to a means and method for printing a print image on both sides of a sheet of paper with the top of the print image on each side being adjacent the same edge of the sheet.
A number of different systems have been proposed for duplex printing. Typically, a sheet of copy paper is fed from a first paper supply station to a printer transport, such as the rotating drum in a xerographic reproduction device, which transports the sheet past a printer at a printing station where a print image is printed on a first side of the sheet. A plurality of sheets may be accumulated in a duplex collection tray after having print images printed on their first sides. In such systems, the sheets are moved past the print station with one of the longer edges of each sheet being the leading edge. Printing is thus accomplished from side to side across a first side of each sheet during the first printing operation, with the first side of each sheet having been originally facing downward at the first paper supply station. In a second printing operation, sheets are fed in succession from the duplex collection tray to the drum with the other of the longer edges of each sheet being the leading edge. The sheets are delivered to the drum in such a manner that the second sides of the sheets, which were facing downward in the duplex collection tray, face the printer at the printing station for printing.
It will be appreciated that where a sheet of paper is presented to a rotating drum for transport past a printer and thereafter the sheet is stored in an intermediate duplex tray, the edge of the sheet which was the leading edge as the sheet moved past the print station and into the duplex tray will be the trailing edge as the sheet is reapplied to the drum. It is inherent in such a system that if the drum is rotated continuously in the same direction, the second side of each sheet is presented for printing during the second printing operation.
A number of such duplex printing systems have been devised, as shown in U.S. Pat. Nos. 3,905,697, issued Sept. 16, 1975, to Komori et al; 3,997,263, issued Dec. 14, 1976, to Stemmle; 4,050,805, issued Sept. 27, 1977, to Hage; 4,099,150, issued July 4, 1977, to Connin; and 4,116,558, issued Sept. 26, 1978, to Adamek et al. In duplex printing arrangements of the type disclosed in these patents, the orientation of the print image is the same during each printing pass. That is, if during the first printing pass, the paper which is transported with one of its longer edges as the leading edge is printed from left to right, the second side of the sheets of paper are also printed from left to right during the second printing pass. The result is that the top of the print image on the first side of each sheet is adjacent the same shorter edge of the sheet as the top of the print image on the second side of each sheet. This print image orientation occurs, however, only when the sheets are transported past the printer with one of their longer edges being the leading edge.
It is desirable to be able to print in a duplex mode on both sides of a sheet of paper utilizing a printer, such as an ink jet printer which prints with successive sheets of paper moving past the printer with a shorter of the paper edges being the leading edge. If such a printer is simply incorporated into prior art printing schemes, however, the sheets so printed will have the print image on the second side of each sheet inverted with respect to the print image on the first side. That is, the tops of the print images on opposite sides of a sheet will be adjacent opposite edges of the sheet. While this may be desirable in certain instances, for example, where the sheets are to be bound across their upper edges, binding the sheets in a booklike format along the left edges of the sheets will not be possible, since the image on the back or second side of each sheet will be inverted.